The long term goal of the proposed research is to investigate the mechanisms that control cell communication during metazoan development. beta-arrestin proteins have recently emerged as multifunctional regulators of several signaling systems. beta-arrestins control signaling networks by associating with specific signaling components and modulating the duration, amplification, and routing of signals inside the cells. Because of their central position in signaling networks, beta-arrestins have been implicated in multiple human diseases, such as schizophrenia, depression, cancer, heart disease, asthma, and diabetes. Despite a large body of work on the signaling activities of beta-arrestins, their biological role in organism development is poorly understood. The goal of the current proposal is to investigate how a single beta-arrestin in Drosophila, Kurtz (Krz), controls two important developmental signaling networks. Preliminary data obtained in Drosophila embryos lacking krz suggest that the Krz protein inhibits the function of two signaling pathways that are active in early development: the receptor tyrosine kinase Torso/MAPK and Toll/NF-&#954;B. Both of these pathways have clinical relevance in several human diseases such as cancer and immunological disorders. Drosophila offers a unique advantage as a genetically tractable and quantifiable system to dissect the role of beta-arrestin Krz in these pathways. Two specific aims will be pursued: 1) To study the role of interactions between Krz and MAPK ERK in the regulation of receptor tyrosine kinase signaling. The main objective of this aim is to identify regions in the Krz protein responsible for its interaction with ERK in a biochemical screening procedure, and to test the functional importance of these regions in receptor tyrosine kinase regulation using in vivo functional assays. An innovative quantitative imaging approach will be used to determine the relative importance of the identified Krz-ERK contact regions for the observed inhibitory effects of Krz on MAPK signaling. 2) To study the mechanisms of NF-&#954;B regulation by Krz. A combination of genetics and novel proteomics strategies will be used to determine the likely mode of regulation of Toll signaling by Krz. The overall strength of the proposed research lies in an integration of genetics, proteomics, and quantitative measurements of mRNA and protein expression patterns. Such a multi-level approach, which is firmly rooted in functional in vivo studies, will likely advance our knowledge of the mechanisms used by beta-arrestins to control developmental signaling pathways, and may suggest new avenues for designing beta-arrestin-directed therapies.